The 3GPP (Third Generation Partnership Project) Long Term Evolution (LTE) standards propose using Orthogonal Frequency Division Multiple Access (OFDMA) for transmission of data over an air interface. In an OFDMA communication system, a frequency bandwidth employed by the communication system is split into multiple frequency sub-bands, or Physical Resource Blocks (PRBs), during a given time period. Each PRB comprises multiple orthogonal frequency sub-carriers over a given number of OFDM symbols, or time slots, that are the physical layer channels over which traffic and signaling channels are transmitted in a TDM or TDM/FDM fashion.
In order to maximize bandwidth usage, OFDMA communication systems may engage in Frequency Selective Scheduling (FSS) or Frequency Diverse Scheduling (FDS). In both FSS and FDS, PRBs are scheduled for a UE on a scheduling period-by-scheduling period basis. For example, in FSS, transmission errors are minimized by scheduling a user equipment (UE) for an PRB only where the UE is known to have a good downlink channel. FSS uses channel feedback from the UE, wherein for any given Transmission Time Interval (TTI) the PRBs are allocated to users based on measured channel conditions. The channel condition measurements are performed by a UE, which UE measures channel conditions for each and every PRB during a measuring period, such as a Transmission Time Interval (TTI) (also known as a sub-frame) or a radio frame transmission period. The UE then reports the measured channel conditions for the PRBs to a serving Node B in a Channel Quality Information (CQI) message. Based on the reported CQIs, an OFDMA communication system then selectively schedules the PRBs over a scheduling period, typically one or more TTIs or radio frames, and further adaptively determines appropriate modulation and coding schemes for each RB during the scheduling period. In FDS, the UE is scheduled for PRBs without channel feedback or only wideband channel feedback, wherein the channel quality reported is over the whole bandwidth and diversity of the PRBs is relied on to minimize transmission errors.
In a 3GPP LTE system, voice data is exchanged via Voice over Internet Protocol (VoIP). Under typical air interface, or radio frequency (RF), conditions in a 3GPP LTE communication system, there is only enough transmit power and frequency bandwidth to make between 6.5 and 8.5 user resource assignments per slot (1 ms), or 6500 to 8500 assignments per second. A VoIP communication session involves a conveyance of 50 data packets per second. For 3GPP LTE systems that are supposed to handle 500 Voice over Internet Protocol (VoIP) users per second, this amounts to 25,000 (500*50) resource assignments per second, which is far more than an available capacity for resource assignment.
To reduce the system capacity consumed by overhead messages such as resource assignments, a Node B may make a “sticky” resource assignment to a user, that is, a resource (for example, PRB) assignment that persists over a period of time, such as multiple scheduling periods, as opposed to being applicable to a single TTI or radio frame. In other words, a “sticky” resource is a dedicated resource that is statically allocated to a user over a period of time and may require de-assignment of the resource in order to assign it to another user. This is as opposed to “time limited,” or “non-sticky,” assignments that have a deterministic expiration time.
“Sticky” resource assignments specify specific modulation schemes, such as QPSK (Quadrature Phase Shift Keying), 16-QAM (Quadrature Amplitude Modulation), and 64-QAM, specific coding rates, such as a ¼ coding rate, a ½ coding rate, a ¾ coding rate, transmit power levels, and so on. However, in a wireless communication system, RF conditions are not static. Changing RF conditions necessitate a change in an allocated resource, such as a new coding rate, modulation scheme, or transmit power level, with the result that shifting RF conditions may lead to potentially frequent changing of “sticky” resource assignments, which again may exceed the available capacity for such resource assignment.
Therefore a need exists for a method and apparatus that better preserves a persistence of a “sticky” resource allocation under shifting RF conditions, reducing the need to change “sticky” resource allocations when RF conditions change.
One of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.